JP2002266270A - Shaft exit assembly to be used in boiler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a shaft exit assembly requiring no liquid discharge from a boiler prior to being put to maintenance service when to be replaced following the maintenance service, and to provide a method therefor. SOLUTION: This shaft exit assembly to be used in a boiler includes a turnable shaft extending from the exit assembly toward the pressure vessel side of the boiler, a packing box attached to the boiler and having a packing around the above shaft, and a seal ring attached to the mobile assembly inside the pressure vessel; wherein it is characteristic that the seal ring has such a shape as to encircle about the shaft, and the mobile assembly occupies a 1st position where the mobile assembly is disposed between the seal ring and the shaft with a slight gap and a 2nd position where the seal ring is pressed against both the shaft and the packing box and a liquid leakproof seal is substantially formed between the packing box and the shaft.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to a shaft outlet assembly used in a digester.

[0002]

BACKGROUND OF THE INVENTION In the pulp and paper industry, as in other process industries, chemical reactions often take place at pressures above atmospheric pressure. Normally, these reactions involve a vessel specially designed to maintain the pressure and temperature required for the reaction,
For example, in a chemical reactor or pulp digester. The process performed, whether batch or continuous, often requires some form of agitation or mixing during processing. This agitation is usually performed with some form of shaft driven agitator. The drive of the stirrer is usually carried out by means of an electric motor via some form of power transmission device, for example a belt, a drive chain or a gear reducer.

[0003]

The drive shaft of the stirrer extends through the wall of the pressure vessel. It is therefore necessary to provide some support structure, for example a sealing device, to maintain the integrity of the container wall through which the drive shaft has penetrated. Some form of sealing device must be provided to prevent the contents of the pressure vessel, especially hot and sometimes harmful contents, from leaking out of the clearance between the usually cylindrical shaft and the opening of the vessel. Must. Also, some form of bearing must usually be provided to reduce the friction between the rotating or reciprocating shaft and the support housing. Usually, the bearings used are roller bearings, for example spherical or cylindrical friction bearings, or journal bearings which are self-lubricating or have the property of reducing frictional forces.

[0004] Seals that prevent leakage of pressurized fluid from around the rotating drive shaft are usually roped knitted fabrics or "packings", or flexible seal rings, or some form of "mechanical" seal arrangement. Done. For example, the packing is usually packed in a fixed cavity or "packing box" or "pack box" located around the shaft and held down by a retaining ring or "gland support". The load on the rotating shaft is supported by fixed packing, which prevents leakage of the contents of the vessel. usually,
To reduce the wear rate of the soft packing, some form of wear resistant material is mixed into the packing. For example, the packing may be a material containing polyethylene terephthalate (PTFE), such as Teflon from DuPont.
(Registered trademark) or graphite.

[0005] The packing is easily worn or broken.
Normally, the packing is inspected and replaced periodically to prevent fluid from leaking from the digester via the packing. In the prior art, when replacing the packing material, it is necessary to open the sealing device between the digester and the drive shaft to access the packing material. In the past, replacing the packing typically required shutting down the digester, reducing pressure, and discharging the fiber slurry. In many cases, the contents of the slurry in the digester must be withdrawn to prevent personal and property damage when servicing such hardware. This ensures that these fluid contents do not flow out of the digester drive shaft during the packing material change. Draining the slurry in a small pressure vessel is less cumbersome than in a large vessel. For example, in a large pressure vessel of a pulp digester, the time and production loss costs of slurry discharge are substantial. For example, in one pulp mill, the cost of extracting liquor from a continuous pulp digester for packing changes can be as high as about $ 1 million.

[0006]

SUMMARY OF THE INVENTION The present invention provides a method and apparatus for servicing and replacing a packing seal used in a digester agitator that does not require drainage from the digester prior to maintenance service. A feature of the present invention is an auxiliary sealing mechanism that does not function during normal operation of the digester, for example, while the shaft is rotating. This auxiliary sealing mechanism is installed to seal the gap between the stopped drive shaft and the drive shaft bearing of the digester when checking and replacing the packing material. By installing this auxiliary sealing mechanism, it is not necessary to discharge the pressurized fluid from the digester to change the packing material.

One aspect of the present invention is an apparatus for preventing liquid from leaking from a tank having a shaft penetrating a container during maintenance service of a packing material for a shaft, for example,
It is a movable seal ring. The present invention provides a mechanism and method that allows the packing to be serviced without emptying the contents of the container. These and other aspects of the invention include:
It will be more apparent from the detailed description of the invention and the appended claims.

The present invention is, in an embodiment, an internally sealed packing box for use in diluting or non-diluting digesters or other pressure vessel outlet devices. This packing box is mounted at the bottom of the digester around the drive shaft used for the outlet device. The packing box comprises a top plate located inside the digester, which is normally held in a non-functional position lifted up. This top plate is the auxiliary sealing device, and performs a sealing function instead of the packing material during replacement of the packing material. To replace the packing material,
The plate is moved downward to form a seal between the housing and the shaft covering the bottom of the outlet device.

[0009] The top plate may include a seal ring having a triangular surface that is pressed against opposing surfaces of the housing and the shaft. The pressure of the fluid in the digester facilitates the formation of a seal, but when pressure is applied to the seal ring, the seal ring is pressed against both the housing and the shaft (by the action of the triangular surface). This is because a seal is formed. This top plate can be attached to a guide rod having a screw. This screw can be turned from the outside of the digester, moving the top plate upward, detaching it from the sealing position, or moving it downward,
It can be adjusted to the sealing position.

A water passage is provided in the ground passage in the housing near the top plate. The water passage is used to flush water flushing the housing surface and the shaft surface with which the seal ring contacts. The water flush is performed during operation and immediately before the top plate is moved to a predetermined position. Furthermore, the fluid pressure in these passages is
After the top sealing plate has been moved to the sealing position, it can be monitored to see if the sealing is successful.

In one aspect, the invention is a shaft outlet assembly for use in a digester. The assembly comprises a rotatable shaft extending from the shaft outlet assembly to the digester pressure vessel; a packing box mounted on the pressure vessel and having packing around the shaft; a seal ring mounted on a plate inside the pressure vessel; Is provided. The seal ring surrounds the shaft and is arranged with a slight gap from the packing box. The seal plate is movable with respect to the pressure vessel and presses the seal ring against the shaft to form a substantially fluid tight seal between the seal ring and the shaft.

[0012] In another aspect of the present invention, a method is provided for servicing packing material of a digester shaft outlet assembly. In this method, the assembly comprises a plate with a seal ring in the pressure vessel of the digester, the seal ring extending around the shaft extending into the pressure vessel of the digester and into the packing box. The method comprises the steps of forming a fluid-tight seal between a shaft and a pressure vessel by packing of a packing box; and moving the sealing plate to press a seal ring against the shaft to maintain the packing. Forming a fluid leakage prevention seal between the ring and the shaft, and using the sealing action formed by the seal ring, replacing the packing material while maintaining the slurry inside the digester under pressure. Moving the shaft to separate the seal ring from the shaft and the fluid-tight seal so that the packing material now forms a seal between the packing box and the shaft;
Rotating the shaft during operation of the digester.In operation, the rotating shaft is sealed with a packing box, but the seal ring is separated from the packing box. .

[0013]

DETAILED DESCRIPTION OF THE INVENTION Although the present invention will be described with reference to what is known in the art as an "outlet device" for use in a continuous digester, it will be understood that the present invention is not limited to the use of a pressure digester. It can be applied to any shaft, whether a container or a non-pressure container, whether a rotating shaft, a reciprocating shaft, or a fixed shaft penetrating the wall of the fluid-containing container.

FIG. 1 shows Glens, New York, USA
Kamis sold by Andritz Inc. of Glens Falls
1 shows the bottom of a yr) ® continuous digester 10. This container is used for continuous chemical pulping of comminuted cellulosic fibrous material, for example, softwood. The comminuted cellulosic fibrous material enters the top of the vessel (not shown) and flows downward while at a pressure higher than atmospheric pressure, typically 0.1-2.
0 bar (104-2 × 106 Pa, 0.1-300 p
si), preferably 5 to 15 bar (5 x 105 to 1.
5 × 10 6 Pa, 70-220 psi) and treated with pulping chemicals at temperatures above 100 ° C., usually 130 ° C. to 180 ° C.

After the pulping reaction is substantially completed,
The pulverized comminuted cellulose fiber material is discharged from the bottom of the digester 10 using a rotating bottom scraper device 11 attached to the bottom mirror 12 of the digester 10. The outlet device 15 is normally driven via a speed reducer 14 using an electric motor 13. In this application, the outlet device is usually 1 to 20 rpm (number of revolutions per minute), preferably 5
Driven at １５15 rpm. However, in other applications, the shaft rotational speed can be higher than these.

The bottom scraper 11 is supported in a pressure vessel (digester) 10 by an outlet device 15. The outlet device 15 includes a bearing for supporting a weight and a load applied to the rotating device, and a sealing device for preventing a process fluid from leaking. With the use of the outlet device 15, it is possible to relatively easily perform maintenance service on the packing seal and other hardware of the outlet device. The outlet device houses a drive shaft 21 (shown in FIG. 2), which drives the bottom scraper 11 at the bottom of the digester. The drive shaft 21 is driven by the electric motor 13 and the speed reducer 14. The outlet support assembly 15 is provided with a coupling through which the drive shaft 21 extends into the pressure vessel of the digester.

FIG. 2 shows a first end having a drive key 29;
2 shows a longitudinal drive shaft 21 with a second end having a second key 31. The drive key 29 is fitted to the bottom scraper 11 shown in FIG. 1, and the second key 31 is fitted to the drive mechanism of FIG. 1, for example, the gear reducer 14. A first end of the shaft resides within the pressure vessel and a second end is located outside the pressure vessel. The shaft 21 rotates around an axis. Exit device 15
Comprises a top housing 22, which is attached to the bottom mirror 12 of the digester 10. The upper surface 52 of the upper housing 22 of the outlet device 15 is open to the interior of the digester and is exposed to pressurized fluid in the digester pressure vessel. The second housing 23 of the outlet device 15 is attached to the upper housing 22 with bolts or studs 32. This housing assembly used for the outlet device 15 has two roller bearing assemblies 24 and 25
And at least one upper packing or seal assembly 26. The upper packing or seal assembly 26 forms an annular fluid-tight seal around the shaft 21. The shaft 21 has one or more liquid deflectors or “flinger” 2
8 can be provided. The flinger 28 protects the bearing assemblies 24 and 25 from leaking liquid falling from above.

Prior to the practice of the present invention, if the packing assembly 26 needs to be serviced or replaced, the pressure of the pressurized slurry contents in the container 10 is reduced and emptied to remove harmful gases. If present, it was necessary to ventilate before servicing. This slurry discharge typically takes 22 to 28 hours before servicing the bearing or sealing device. During this long-term maintenance service, the digester is shut down for the entire period and no pulp is produced. When such prior art work is performed, resulting in losses in the pulp production of the digester, the pulp output is reduced to $ 1 million (20 million).
Costs (in dollars of 2001).

According to the present invention, the packing assembly 2
In the maintenance service and replacement of 6, the pressure can be reduced and emptied, and even when harmful gas is present, it can be performed without ventilating the digester. To prevent leakage of the fluid from the digester during maintenance of the packing of the packing assembly, the auxiliary seal device 36 is tightened in place and the shaft 21 and the bearing wall surface of the housing 22 of the outlet device 15 are tightened. Seal the gap between. The auxiliary sealing device 36 is located on the pressure vessel side of the digester 10. This auxiliary sealing device 36
When the digester is in a normal operation state, it is detached from the sealing position, for example, by pushing an auxiliary sealing device, for example, an auxiliary sealing plate above the sealing position. If the packing needs to be serviced, the sealing device 36 is lowered to the sealing position (arrow 7 in FIG. 3).
If the shaft 21 is pressed against the outlet device 15 and sealed, the digester fluid does not leak from the sealing device 36. If the auxiliary seal device 36 is tightened and set at a predetermined position, the packing 26 and the packing land 46 can be taken out and the packing 26 can be serviced.

FIG. 3 is a partial sectional view showing the portion B in FIG. 2 in detail. The shaft 21 is rotatably attached to a cylindrical opening area of the upper housing 22. The toroidal sleeve 40 which is fitted and rotated by a key on the shaft 21 is provided with a packing material 26 (shown as a box with a cross in the box in FIG. 3) in an annular gap 42 between the housing 22 and the shaft 21. Is in contact with the rotating surface. The rubbing between the packing material 26 and the sleeve 40 forms a fluid leakage prevention seal that allows fluid from the digester to flow out around the shaft 21 and to reduce the pressure of the digester around the shaft 21. Flow from the container side is prevented. A packing material, such as a rope braid, a flexible seal ring, or some form of "mechanical" seal arrangement is contained between the gland bushing 44 (at the top end of the packing) and the packing land support 46. . Packing land support 46 is packing 2
6 is an annular flange at the bottom. Packing material 26
To replace the gland 46, the gland 46 is slid downward along the shaft 21 and removed to access the packing material 26 from outside.

Before replacing the packing material 26, the auxiliary sealing device 36 is moved to bring the shaft 21 and the upper housing 22 into a sealed state. Auxiliary sealing device 3
6 is an annular seal ring 5 surrounding the circumference of the shaft 21
0 is provided with a movable plate 66. When the packing material 26 is to be replaced, the auxiliary sealing device 36
The seal ring 50 is lowered and tightened between the shaft 21 and the sleeve 40 of the shaft 21 and the housing 22.
Between the housing 22 and the shaft 2.
A fluid-tight seal is formed in the cylindrical opening between the first sleeve 40 and the first sleeve 40. The seal ring 50 has a triangular nose 54 and an upper sleeve 56 in cross section. Nose 5
4 has opposing sealing surfaces 58 and 60, each of which has a tapered surface 62 on sleeve 40 and a tapered surface 64 on housing nose 65.
And contact each other. The tapered annular surface 62 on the sleeve 40 is at the top outer edge of the sleeve 40 and
Mates with the surface 58 of the zero nose 54. Similarly, the tapered surface 64 on the housing nose 65 is at the top inside edge of the cylindrical opening 40 provided for the drive shaft 21.

The seal ring 54 does not scratch, adhere, or otherwise damage the metal surface of the shaft, sleeve, or housing. The seal ring can be made of Teflon or other relatively soft material. The attachment of the seal ring 54 to the annular top plate 66 of the auxiliary seal device 36 can be performed with bolts 68 or other attachments. The lower inner surface 70 of the top plate 66 is shaped to fit with the seal ring 54, and the seal ring 54
Is held. The upper surface of the top plate 66 is exposed to the fluid pressure on the pressure vessel side of the digester, and pressure from the fluid side acts downwardly on the seal ring 54 from this plate 66 (when the ring is in the sealed position). Therefore, the fluid leakage prevention seal of the seal ring 54 is held by the aid of the fluid pressure in the digester.

The top plate 66 and the seal ring 54 are mounted inside the vessel of the digester. During normal operation of the digester, the top plate 66 is in the pushed up position,
Seal ring 54 does not mate with tapered surfaces 62, 64 of sleeve 40 or upper housing nose 65. An arrow 71 generally indicates an operation in which the top plate 66 and the seal ring 54 move up and down. This operation must be relatively small. The only purpose of operation is to seat and unseat the seal ring 54 against the tapered surfaces 62, 64 of the sleeve and housing. A pull-down rod 72 can be attached to the top plate 66. The pull-down rod 72 has a screw which can be turned from the outside of the digester to push the top plate up and away from the sealing position or down to the sealing position. Although one pull-down rod 72 is shown in FIG. 3, this is for explanation only. In practice, two or more pull-down rods can be used symmetrically around the shaft 21. The operation of the top plate 66 is performed by a pull-down rod 72 attached to the top plate 66 and extending through an opening 74 of the housing 22.
If it is provided, it is possible to prevent the digester fluid from leaking from the rod opening. The bottom of the rod 72 can be threaded and allow the nut 78 to pass through. Rotating the nut 78 moves the rod 72 (and thus the top plate 66) up and down.

The ground passage 80 in the housing 22 near the top plate 66 is a water passage, and this water passage is
It is used to flush the flushing and flushing of the housing surface and the shaft surface with which the seal ring contacts.
This water flush is performed immediately before the top plate 66 is moved to bring the seal ring 54 into the sealing position. In addition, the pressure of the fluid in these passages can be monitored with a pressure gauge 86 to determine whether the seal is being properly sealed after the top seal plate 66 has been moved to the sealing position. The water source 82 can be connected to the ground passage 80 via a pipe 84. Similarly, a drain pipe 88 can be connected to the pipe, which is controlled by a valve 90.

FIGS. 4 and 5 are flowcharts showing the operation of the auxiliary sealing device. During operation, the packing material 26 is replaced after the auxiliary sealing device 36 has been moved to the sealing position. Before the auxiliary sealing device 36 is moved to a predetermined position, for example, the shaft 21 of the outlet device 15 is stopped in step 1001, but the liquid is not discharged or the pressure is not reduced. Step 1002 is to check whether the water line 80 connected to the packing box is clogged.
To check.

The flow of the seal water flowing into and out of the bottom of the packing box and the water pressure are checked, and it is checked in step 1003 whether a line (for example, the pipe 84) for supplying, returning, and discharging the seal water is blocked. Step 1
At 004, water flushing is performed through the ground water passage 80 to clean away the area around the seal ring 54, and that no debris or the like is accumulated on the contact surfaces of the seal rings 58, 60, the sleeve surface 62, and the housing surface 64. Ensure that the fluid leakage seal can be formed immediately.

At step 1005, the top seal plate 66 is lowered by turning the nut 78 and lowering the rod 72 while the flush water is kept flowing.
4 is lowered to the sealing position between the sleeve surface 62 and the housing surface 64. When turning the nut 78, it is necessary to adjust it so that the level of the seal plate 66 is securely raised. When the sealing plate 66 is inclined (off-level), the mounting rod 72 is connected to the rod opening 74.
The seal ring 5
4 may not form a good seal. As the seal ring 54 fits into the sleeve 40 and the housing 22 in step 1006, the seal ring 54 closes the outlet of the gland water passage 80 and the flow of water flush decreases, so the final flush in step 1007 Stop the flow. The time when the flow of the water flush becomes zero is when the shaft and the housing are properly sealed by the seal ring. If the flow of the water does not stop, at step 1008, the sealing plate 66
Can be raised and then lowered again to reseat the seal ring on the packing housing.

When the flow of water is stopped, the torque applied to the nut of the pull-down rod 70 is at a predetermined level, for example,
Must be 110 foot-pounds. If the torque level is high, for example, reaching 110 ft-pounds (about 0.15 Nm), and the flow of water flush is continuing, then the seal ring is not properly seated and step 1009 is performed. It is necessary to reverse the rotation of the nut 78 to lift the seal plate 66.

After the seal ring is properly seated and the flush water flow is zero, the water source 82 is closed, the water pressure is reduced at the drain 88, and the pressure at the bottom of the seal ring is released. This is step 1010. Once the water is drained, the drain 88 is closed (step 1011), a safety check is performed on the pressure sensor 86, and it is confirmed in step 1012 that there is no fluid pressure in the pipe 84 connected to the flush water ground passage 80. . If there is pressure in this passage, the seal ring is leaking and the sealing process must be restarted. Thereafter, the pressure on the seal ring is only a completely downward pressure. This is because only a force due to the tension of the mounting rod 72 and the fluid pressure in the vessel of the digester is applied.

If the pressure safety check confirms that the seal ring is not leaking, the packing material 26 can be accessed from outside by pulling down or removing the packing land support 46 at step 1013. The plurality of rings of the packing material 26 are removed at one time. While removing each packing ring, monitor pressure sensor 86 to check that pressure is not being generated in flush water gland passage 80. The pressure in this passage 80 during repacking indicates that the seal ring 54 is leaking, and the packing 26 and gland 46 must be reassembled immediately. After confirming that all the rings of the packing material 26 have been removed, install a new packing ring 26, slide the gland 46 back around the shaft 21 and the sleeve 40, and complete step 1014, the reattachment process. When the replacement and replacement of the packing material is completed, the nut 78 is turned to raise the seal plate 66 to release the seal between the seal ring 54 and the tapered surfaces 62, 64 of the sleeve 40 and the housing 22. This is step 1015. When the digester is restarted, the auxiliary seal plate and the seal ring are held up, the shaft 21 starts rotating, and normal operation is resumed. The digester remains pressurized with the slurry fluid throughout the reloading process.

The outlet device described above is not limited to a device applied to a continuous digester. The present invention can be applied to other pressure vessels in which leakage may be caused by penetrating the shell of the vessel. The outlet device is particularly used in a tank for processing the comminuted cellulose fiber material, for example, a continuous digester, a batch digester, an infiltration tank, or a washing tank, other pretreatment tanks including a bleaching tank, and a post-treatment tank. It can be applied regardless of whether it is pressurized or non-pressurized.
The outlet device may also be a pressurized or unpressurized vessel having a device for introducing material into the vessel, for example, Andritz (Andritz)
ritz Inc. 2.) Applicable to conventional top separators for sale, or other forms of agitators. The outlet device can also be used in mixers, deaerators, or internally inserted instruments, such as digester level indicators.

Since the present invention has been described in what is presently considered to be the most practical and preferred embodiment, the invention is not limited to the disclosed embodiments, but, on the contrary, the spirit of the invention and the claims Should be understood to include all the partial modifications and equivalent configurations included in the scope of the above.

[Brief description of the drawings]

FIG. 1 is a partial perspective view of a prior art tank with a shaft, a shaft operating component, and a shaft support component, partially cut away for clarity.

2 is a detailed side view of region A of FIG. 1, partly in section and partly in elevation, the shaft of the structure of FIG. 1;
It is a figure which shows the container of the place which fits a shaft.

FIG. 3 is a detailed side view of region B of FIG. 2, partly in cross-section and partly in elevation, showing an exemplary embodiment of the packing and auxiliary sealing mechanism.

FIG. 4 is a flowchart of exemplary steps for using an auxiliary sealing device while changing packing material.

FIG. 5 is a flowchart of exemplary steps for using an auxiliary sealing device while changing packing material.

[Explanation of symbols]

10: digester, 11: bottom scraper, 12
... Bottom mirror section, 13 ... Electric motor, 14 ...
Speed reducer, 15 outlet device, 21 drive shaft, 22 upper housing, 23 second housing, 24, 25 roller bearing assembly, 26 packing assembly, 28 ... Drainer (flinger), 29 ... Drive key, 31 ... Second key, 32,68 ... Bolt or stud, 36
..Auxiliary sealing device, 40...
42 ... annular gap, 44 ... ground bush, 4
6 packing land, 50 ring seal ring, 54 triangle seal ring nose, 56 upper sleeve, 66 movable plate, 58, 60 seal surface, 62, 64 ... tapered surface, 65 ... housing nose, 70 ... inner surface, 71 ... arrow, 72 ...
・ Pull down rod, 74 ・ ・ ・ Rod opening, 76
... Seal ring, 78 ... Nut, 80 ... Gland passage, 82 ... Water source, 84 ... Piping, 86
..Pressure gauge, 88 ... water drain.

Continuation of the front page (72) Inventor John Dee. Weston United States, 12804 New York State, Queensbury, Tathill Road R2 (72) John F. Inventor. Boles United States, 12804 New York, Queensbury, Maple Drive 24F Term (Reference) 4L055 AC06 CA31 CA40 FA22 FA30

Claims (20)

[Claims] 1. A shaft outlet assembly for use in a digester, comprising: a rotatable shaft extending from the outlet assembly to a pressure vessel side of the digester; and a packing box attached to the digester, around the shaft. A packing box having packing therein, and a seal ring attached to a movable assembly inside the pressure vessel, wherein the seal ring has a shape surrounding the shaft, and the movable assembly includes:
A first position, which is arranged with a slight gap between the seal ring and the shaft, and wherein the seal ring is pressed against the shaft and the packing box, and a substantially fluid-tight seal between the packing box and the shaft. A shaft outlet assembly occupying a second position forming the shaft exit assembly. 2. The invention according to claim 2, wherein said shaft has an annular end surface facing said seal ring, said annular end surface mating with said seal ring when moving said movable assembly plate relative to a pressure vessel. The shaft outlet assembly according to claim 1, wherein: 3. The shaft exit assembly according to claim 2, wherein said shaft comprises a tapered annular surface that contacts said seal ring when said movable assembly occupies a second position. 4. The shaft exit assembly according to claim 3, wherein said tapered annular surface is attached to a sleeve of a shaft. 5. The shaft exit assembly according to claim 1, wherein said packing box has a tapered annular surface for receiving said seal ring. 6. The shaft outlet assembly according to claim 5, wherein said annular ring at the plate edge is scored. 7. The seal box of claim 1, wherein the packing box has an annular surface facing the seal ring, the annular surface mating with the seal ring when the shaft is lifted up. Shaft outlet assembly. 8. The shaft outlet assembly according to claim 7, wherein the annular surface of the packing box includes at least one protrusion that engages with the seal ring when the shaft is lifted up. 9. The shaft outlet assembly according to claim 1, wherein the digester receives a slurry of comminuted cellulosic fibrous material from the top separator. 10. The shaft outlet assembly according to claim 1, wherein said rotatable shaft extends through said top separator to said digester. 11. The shaft outlet assembly according to claim 1, wherein the seal ring is formed of a soft sealing material. 12. The shaft outlet assembly according to claim 1, wherein said seal ring is an annular body having a substantially trapezoidal cross section. 13. The seal ring has an upper surface portion and a lower surface portion, wherein the upper surface portion of the seal ring faces a lower annular surface of the packing box, and the lower surface portion of the seal ring is formed of the shaft. The shaft exit assembly according to claim 1, wherein the shaft exit assembly is opposite the annular end. 14. The seal ring further comprising an inner cylindrical surface mounted to an annular surface of the shaft, wherein the annular surface is near the end of the shaft. The shaft outlet assembly according to claim 6. 15. The shaft exit assembly according to claim 1, wherein said shaft comprises a shaft sleeve, said sleeve comprising an end supporting said seal ring. 16. A method of servicing packing material of a digester shaft outlet assembly, the assembly comprising a plate with a seal ring in a pressure vessel of the digester, wherein the seal ring is located in the pressure vessel of the digester. And extending around a shaft extending to the packing box, the method comprising: (a) forming a fluid tight seal between the shaft and the pressure vessel by packing of the packing box; (b) Moving the seal plate to press the seal ring against the shaft to form a fluid-tight seal between the seal ring and the shaft for servicing the packing;
(C) using the sealing action formed by the seal ring to replace the packing material while keeping the inside of the digester in a slurry state under pressure; and (d) moving the shaft to remove fluid from the shaft. Removing the seal ring from the leak-proof seal and allowing the packing material to form a seal between the packing box and the shaft; and (e) rotating the shaft during operation of the digester. A shaft outlet assembly maintenance service method, wherein the rotating shaft is sealed by a packing box during operation, and the seal ring is separated from the packing box. 17. The method of claim 16, further comprising detecting a fluid pressure in the packing box before lifting the shaft. 18. The method of claim 16, wherein the fluid pressure is monitored while lifting the shaft.
The method described in. 19. The method of claim 16, further comprising the step of not performing steps (a) to (d) if the detected fluid pressure exceeds a predetermined packing fluid pressure. ) 20. The method of claim 16, wherein the shaft is not rotating during steps (a)-(d).